The present invention relates to a brake fluid pressure control valve or valve assembly for use in an automotive vehicle, and more particularly, to a fluid pressure control valve of the type which senses deceleration rate or degrees of a vehicle for supplying a braking hydraulic pressure suitable for the deceleration rate to the rear wheel cylinders.
As a vehicle in running is supplied with an excessively high hydraulic pressure to the rear wheel brakes, the rear wheels are more likely to be subjected to locking, thereby giving rise to slipping, which often leads to a so-called dangerous skidding phenomenon in addition to a degradation of the braking effect. For avoiding this dangerous locking of the rear wheels it has been practiced to dispose a braking hydraulic pressure control mechanism in the rear brake circuit connecting the master cylinder and the rear wheel cylinders for the purpose of controlling the hydraulic pressure applied to the rear wheel cylinders.
Toku-Kai-Sho-48-54382, laid open in Japan in 1973, is one of the well-known examples of this type. This is a controlling valve of the type for controlling the operative pressure of the braking hydraulic pressure control valve thereby supplying a proper braking hydraulic pressure, corresponding to the load condition of a vehicle, to the rear wheel cylinders, (a) by means of combining (i) a braking hydraulic pressure control valve in which the outlet port pressure keeps the same rate of increase as the inlet port pressure while the inlet port pressure is less than a predetermined value and the outlet port pressure increases, when the inlet port pressure exceeds the predetermined value, at a rate of increase less than the that of the inlet port pressure or at a rate equal to zero, just in a similar way to that of a proportioning valve or a limiting valve, and (ii) an inertia valve, generally called a gravity valve, which interrupts a fluid passage when the rate of vehicle deceleration exceeds a predetermined value; and (b) by means of effectuating a controlled hydraulic pressure by the inertia valve, on a first plunger of the braking hydraulic pressure control valve, through a second plunger and a spring member.
The control valve introduced above is in fact an excellent device which enables the characteristic curve of the rear wheel cylinder to be almost of an ideal form and thereby enables to assure a proper distribution of the braking force, in response to the load condition of a vehicle, between the front and rear wheels. Although it shows such a superior effect, it is still not perfectly free from a disadvantage, that is, a considerably large amount of braking fluid being necessary, which means an increase of the brake pedal stroke.
The aforementioned disadvantage can be attributed to the following reasons: (1) This control valve attempts in principle to control the actuating pressure of the braking fluid by means of varying the resilient force of a spring member applied on a plunger of the braking hydraulic pressure adjusting valve. (2) For controlling the actuating pressure over a wide range, it is required for the spring member to be largely compressed. (3) Large amount of the spring compression requires in turn an elongation of the travel distance or stroke of the plunger therefor, which is inevitably accompanied by an increase of the amount of the fluid employed therefor.
The disclosure of Sho-49-58280, laid open in Japan in 1974, is known as an attempt to solve the above problem. The basic principle of this attempt resides in that: (a) by means of disposing a third plunger which fluid-tightly and slidably passes through the second plunger for the compression of the spring member, which third plunger is to be placed in direct abutment on the plunger of the fluid pressure adjusting valve; and (b) by means of rigidly transmitting a part of the force, which is required for controlling the actuating pressure of the hydraulic pressure adjusting valve, not through the compression of the spring member; it aims a reduction of the fluid amount employed through the reduction of the compression amount of the spring member.
Several other disclosures further improved, based on this concept, have been published such as, 49-58281, 49-116468, 50-24677, 50-63371, etc., all laid open in Japan. A disadvantage common in those disclosures can be characterized in that the fluid pressure valve of this kind will not be actuated before the inertia valve is closed, because the third plunger passing through the second plunger is in direct contact or abutment with the plunger of the fluid pressure adjusting valve, and the pressure receiving area of the former (the third plunger) is equal to or larger than that of the latter (pressure adjusting valve) plunger. This disadvantage consequently leads to narrowing of the design freedom, or restricting of the free designing, and to an enlargement and/or a complication of the construction.
It is therefore an object of this invention to provide a control valve simple in construction, less in the fluid amount employed, having a broad freedom of designing based on a different concept for solving the problem from the disclosure of Sho-49-58280 and others, and further improved by eliminating the weakpoint or disadvantage of Sho-48-54382 invention.
It is another object of this invention to provide a control valve of the type in which the actuating point of a so-called proportioning valve is to be controlled by a so-called gravity valve whereby a proper distribution of the braking force, in accordance with the load condition of a vehicle between the front and rear wheels is performed, and in which the reduction of the fluid amount employed can be achieved.
It is still another object of this invention to provide a control valve of the type in which the actuating point of a so-called limiting valve is to be controlled by a so-called gravity valve whereby a proper distribution of the braking force, in accordance with the load condition of a vehicle, to the front and rear wheels is performed, and in which the reduction of the fluid amount employed can be achieved.